Antifouling paints employing an organotin copolymer and forming a coating film which gradually dissolves away in seawater are excellent in the ability to prevent the attachment of marine organisms to the surfaces of ship bottoms, etc., but the use thereof is restricted in recent years because of the problem of sea pollution.
As a coating composition for eliminating the sea pollution problem is widely used an antifouling paint employing rosin as a soluble resin. Antifouling paints employing polymers containing various hydrolyzable groups incorporated therein have also been proposed. However, these antifouling paints all have not been put to wide practical use. Among those antifouling paints is, for example, an antifouling paint of the hydrolyzable self-polishing type proposed in WO 84/02915 and JP-A-63-215780 which employs a (meth)acrylic ester polymer having triorganosilyl groups in side chains or a similar polymer. (The term "JP-A" as used herein means an "unexamined published Japanese patent application.")
The present inventors made intensive studies on coating films of such an organosilicon containing polymer. As a result, it was found that the antifouling paint employing a polymer modified by only incorporating triorganosilyl groups in side chains of the molecule as described in the above-cited reference has problems such as the following: (1) the coating film does not: show erosion in the rotary test which is the most important test for evaluating hydrolyzable antifouling paints (a test for measuring coating film thickness reduction as erosion rate! in which test pieces are fixed to the outer circumferential surface of a cylindrical drum and the drum is rotated in seawater at a peripheral speed of 16 knots); (2) the coating film does not exhibit satisfactory antifouling properties in exposure test .(immersion test); and (3) the coating film develops cracking and shows poor adherence to the substrate or primer coat, so that it peels off when immersed in seawater. Thus, the antifouling paints of the above-described kind do not have properties required for antifouling paints.